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Very Large Maps, is it a problem?

Hello all. I want to make a world map of a planet similar in size to Earth. I've read some tutorials here (which were very helpful) and I think I have the basics down on how to actually make a map. Fiddling around with a map the size of 4000x2000 however, I found out there weren't enough pixels for me to add any detail to it.

Since it seems 1 mile=1 px is the standard around here, I'm wondering if I can create a map of something like 20,000x10,000 px (or perhaps even 40,000x20,000, though that is perhaps not necessary) without my computer starting to lag. I tried it briefly just zooming and drawing a little, and it worked very well. Will that stay true once I add tons of layers and other things to the map as well?. It's at this point only for my own reference and understanding and will be in black&white, if that makes any difference.

Very cool forum though, I never thought there would be a community dedicated to precisely what I was looking for when I started searching for tips on how to make fantasy maps. This was more than I had hoped for

More layers = slower performance. The main thing is to see just how big you can go. I can do 25,000 x 12,500 on my machine albeit with major slowdown. I routinely do under 10,000 with ease. Just pick a size, try it and see what happens.

If the radiance of a thousand suns was to burst at once into the sky, that would be like the splendor of the Mighty One...I am become Death, the Shatterer of worlds.
-J. Robert Oppenheimer (father of the atom bomb) alluding to The Bhagavad Gita (Chapter 11, Verse 32)

Layers and groups of layers and layer effects make a huge difference.. what i did on my recent map of Gotha, which is 15000 X 7500 (about 2mi/px at equator), was to keep data elements or things that i may want to edit later and in separate layered files from the master. For instance all of my rivers are on several layers depending on size.. and i'd keep them in another file with a flattened terrain map as the background so i can see what i'm doing when i edit. Then i bring over the rivers to the main file and flatten them as a layer rather than having another group. Later if i want to change the rivers for some reason i trash the layer in the main file and go to my rivers file and change it then drag over and flatten again. I do the same thing with climate, rainfall, masks etc.. bring them over when i need them, use them for that purpose and then delete them from the main file. Better to take up hard disk space with separate manageable files (preferably on a peripheral drive) than to clog up your ram with a huger than necessary document. Cuts down on time for screen refresh and applying effects.

Something else i have picked up is having two files... one labeled filename_backup which i'll save out to occasionally. With work that big saving can take a while and you never know when something might glitch and freeze up.. at least you'll have an extra file rather than one corrupt file!

Another thing you may want to do is build all of you continents seperately, so you are only generally working with maps 1/4 to 1/8 of your desired world size. When you have finished all of your continents, make your 40000x20000 blank canvas, and add your continents to it. This way you only have to deal with slow down for the final stages of your map as opposed to getting decreased performance the longer you work on it.

I find this discussion very interesting, cause you guys are talking about all this huge image size, but what dpi are you running it at? cause I ran a 3000x15000 300dpi (mind you I don't have the greatest computer) and it was running at a decent rate, faster than some large files I've ran... but just wondering, cause if your doing a 12,000x10,000 at 72 dpi thats a lot different than 300 dpi =D

I've had to break up into smaller manageable files at times, when the map had way too many layers for the size I was running it at, so that does help out a ton, excellent suggestions from everyone so far!

The resolution is nothing more than a bit of metadata that suggest how large the image should be displayed or what size scanned/sampled. A 20k x 40x raster is a 20k x 40k raster regardless of whether you have a little tag that says 72dpi, 200dpi, or 20m/px.

Yes.. Hai Etlik is right.. 15000 pixels is 15000 pixels.. period.. displaying more of them in an inch means shrinking the apparent size (visually) but not the document pixel content.. and would be dictated by what the image is going to be used for.

There's a stickied discussion in the General Forums on the difference between DPI and PPI, its worth a look, based on some of the discussion here. But to answer your question, it really depends on what software you are using. Sounds like Photoshop or GIMP, both with lots of layers and pixel area are problematically slow. That's why I use a vector app with robust image handling capability, Xara Xtreme, and that I create most of my maps with the intention of printing - as I run Gamer Printshop and specialize in printing large format maps. If you're using an image editor and using lots of layers, performance will go down, its how the application manages memory.